1. Field of the Invention
The present invention relates to an interleaver for an optical communication system, and more particularly to an interleaver for an optical communication system, which is capable of reducing optical loss together with ensuring precise optical axis alignment and easy adjustment of a channel gap when separating channels for transmission of optical signals in WDM (Wavelength Division Multiplexing).
2. Description of the Related Art
Among the multiplexing methods for optical communication, WDM (Wavelength Division Multiplexing) uses a method of dividing signal channels and transmitting data without installation of an additional optical cable. Thus, WDM allows easy channel expansion and is suitable for communication networks capable of high speed and bulk transmission.
However, in case of WDM, if a communication standard is once fixed as, for example, DWDM (Dense Wavelength Division Multiplexing) of about 100 GHz or 200 GHz or CWDM (Coarse Wavelength Division Multiplexing) requiring to keep a channel gap of 20 nm, a system is configured using optical elements suitable for the standard. Thus, in order to use a new channel wavelength by setting an existing channel gap narrower, there should be provided an interleaver to be newly used in the overall signal channels for separating signal channels as shown in the waveform of FIG. 1. When such an interleaver is used, it is possible to adjust bands from 100 GHz to 50 GHz, or from 200 GHz to 100 GHz, or a channel gap from 20 nm to 10 nm. Thus, the interleaver may expand an effective channel region of WDM substantially in double.
U.S. Pat. No. 5,809,190 discloses a conventional configuration for an interleaver. In the US patent, two strands of optical fibers 41 and 42 are mutually fused so that a light advancing along one optical fiber 41 is partially moved to the other optical fiber 42, thereby enabling to obtain periodic filter characteristics by means of change of the intensity of light in correspondence to wavelength of an optical signal (see FIG. 2).
In addition, as another example of a conventional interleaver, U.S. Pat. No. 6,169,626 discloses a technique that employs the Michelson interferometer (see FIG. 3). This technique uses a method of selectively filtering wavelength of a corresponding signal according to constructive or destructive interference corresponding to phase difference of light by use of interleaver components 810 and 820 respectively provided with a beam splitter and a mirror.
However, the aforementioned interleaver technique employing the fusing method is not easy to ensure thickness representation and maintain an isotropic shape during welding, so it has weak points that polarization may be deteriorated and tolerance is small in optical axis alignment. In case of the interleaver technique employing the Michelson interferometer, a half of light returns toward a light input port, so it should be resigned to 3 dB optical losses. Thus, there is still a need to develop an interleaver with a new configuration capable of solving the problems.